Mounting of meshes in discharge devices



Jan. 29, 1957 A. E. JENNINGS 2,779,887

MOUNTING OF MESHES IN DISCHARGE DEVICES Filed May 18, 1953 ALBERT EDWARD JENN/NG MOUNTING F MESHES IN DISCHARGE DEVICES Albert Edward lennings, Hayes, England, assignor to Electric & Musical Industries Limited, Hayes, England, a company of Great Britain Application May 18, 1953, Serial No. 355,643 Claims priority, application Great Britain May 2.8, 1952 3 Claims. (Cl. 31366) This invention relates to the mounting of meshes in the envelopes of discharge devices, and especially but not exclusively to the mounting of meshes in the envelopes of television pick-up tubes lof the kind adapted to operate with cathode potential stabilisation.

One construction of pick-up tube of this kind is described in Journal of the Institute of Electrical Engineers, volume 97, part lll, No. 50, and according to this construction the tube is provided with `a target which comprises a mosaic screen in the form of a multiplicity of discrete photo-electrically sensitive elements. ln the manufacture of such a tube, the mosaic screen may be formed by evaporating metal to form said elements through a mesh mounted, to act as a stencil, in close contact with lthe surface in the `tube envelope on which the mosaic screen is to be formed. Moreover, in the specification of U. S. Patent No. 2,507,958 it has been proposed to mount a mesh in such tubes in front of but spaced a small distance from the mosaic screen. Therefore it would be desirable to be able to move the mesh used as a stencil to serve subsequently as the stabilising mesh. However,` with some metals used to form mosaic elements exposure to air Iafter the deposition of the metal produces harmful 'eiiects, and the use of the same mesh as a stencil and a stabilising mesh then involves moving the mesh a small critical distance without having access to the interior of the tube envelope and in practice diiiiculty has been experienced in so moving the mesh.

A similar diliiculty may be encountered in other cases where it is desired to move `a mesh within the envelope of a discharge device at some stage during its manufacture or operation.

The object of the present invention is to reduce the diiiiculty aforesaid.

According to the present invention there is provided a mesh such as can be used in the envelope of a discharge device, the mesh being mounted for movement between two limiting positions, and provided with means for holding the mesh resiliently in one of said positions so that the mesh can be dislodged and moved to the other limiting position by shock said means being such as to lock the mesh automatically in the other limiting position when the mesh is moved thereto.

In order that the said invention may be clearly understood and readily carried into effect, the same will now be more fully described with reference to the accompanying drawings, in which:

Figure l illustrates a sectional view of a fragment of the envelope of a television pick-up tube in accordance with one example of the present invention, a section being taken on the line I-I of Figure 2,

Figure 2 is a plan view of the fragment of the envelope shown in Figure 1,

Figure 3 is a sectional elevation, on an enlarged scale, taken on the line III-I1I of Figure 1, and

Figure 4 is a View similar to Figure 3 showing parts moved to a diierent position.

Referring to the drawings, it will be assumed that the States Patent O ice invention is applied to a pick-up tube of the kind described with reference to Figure 6 in the aforesaid publication. The fragment includes an end wall 1 of the tube and illustrates a stage in the manufacture of the tube at which a conductive film 4 on a thin sheet oi': dielectric material 3 such as glass or mica has been applied to the end wall 1 to form respectively the signal plate of the tube and the surface on which the mosaic screen is to be deposited. At this stage in the manufacture of the tube a stainless steel frame 2 is mounted on the end wall 1 in contact with the sheet of dielectric material 3. As shown in Figures l and 2 the trarne 2 has side limbs 5 with inturned flanges 6, the flanges being provided along the edges of the side limbs 5 remote from the sheet 3. The frame has, moreover, end iianges 7 which have :apertures for receiving pins 8 fused in the end wall of the tube, the frame being fixed securely in position by means of clips on the projecting ends of the pins. The frame 2 acts as a mounting for a second, relatively massive frame 9 of copper which as shown lits between the sheet 3 and the iianges 6. A metal mesh 10 of fine pitch is stretched on the frame 9, this mesh, as will hereinafter appear, serving as a stencil duii'ng the production of the mosaic screen of the tube and subsequently serving as a stabilising mesh. Pins 11 project from the sides of the frame 9 and ride in guide slots 12, one of which is shown in Figures 3 and 4, in the sides 5 of the first frame 2, the pins 11 projecting to the yexterior of the frame 2. At the exterior of the frame 2 the pins 11 co-operate with arms 13 pivoted by rivets 14 to the sides 5 lof the frame 2. The arms 13 have rearward extensions 15 which are engaged by a spring wire 16 secured :as shown to one of the flanges 7, tending to cause the arms to pivot in the clockwise direction as shown in Figures 3 and 4.

When the frame 2 Aand the mesh supporting frame 9 are first mounted in the tub-e, it is arranged that the frame 9 assumes the position shown in Figure 3 in which the mesh 10 is pressed against the surface of the sheet 3 by virtue of the downward pressure exerted on the pins 11 by the spring loaded arms 13. After the frames 2 and 9 have been so arranged, the tube is exhausted and electrostatic force is applied to the mesh 10 to pull it into intimate contact with the sheet 3 in the manner described in the specification of U. S. Patent No. 2,600,121. Thereupon meta-l is deposited on the sheet 3 by evaporation of metal through the interstices of the mesh 10 in known manner to form the conductive elements of the mosaic screen, the mesh thus serving its function as a stencil. The electrostatic force is removed, the conductive elements are sensitised in known manner by the admission of caesium and in some cases oxygen, and the envelope of the tube is then sealed oil the pump. Thereupon, lthe tube is shaken or given a light blow, for example with the palm of the hand, in such manner as to tend to cause the relatively massive copper frame 9 to move in the direction away from the surface 3. Since the frame 9 is only held by the action of the spring 16 against such movement, the

p movement readily occurs. The pins 11 then ride along the slots 12 until the mesh reaches an outer limiting position which is defined by the iianges 6. When the frame 9 reaches this position the pins 11 have passed the points 17 in the arms 13 and the arms are free to pivot downwardly past the pins 11 into the position shown in Figure 4, under the action of the spring 16, the inclination of the slots 12 in relation to the edges 18 of the arms 13 now being such that the action of the spring 16 is to press the frame 9 against the flanges 16. When the arms are in this position the frame 9 is positively locked in position and cannot be dislodged by such vibration or shock as is likely to be encountered in normal usage ofthe tube. Moreover, when the frame 9 is in this position the spacing between the mesh 10 and the sheet 3, on which the mosaic screen has now been provided, is accurately determined by the anges 6, so that the critical spacing which is required between the mesh and the mosaic screen, if the former is to function as a stabilising rnesh as described in the speciiication of U. S. Patent No. 2,507,958 can be readily established.

In a practical example `of the invention, the angle between the edge 18 of the arm 13 and the radius from the pivot 14 to the point i7 is 90. This angle has been indicated as A in Figure 4. The slots 12 are inclined at 45 to the plane of the mesh. Moreover the arms i3 are such that when the mesh in its router limiting position, i. e. against the anges 6, the distance from the point 17 on each arm 13 to the point of contact 19 between the corresponding pin 1i and the arm 13 is small. It will be :appreciated that when the mesh is in the outer limiting position i. e. against the ilanges 6, and `a force is exerted on the mesh tending to move it away from the flanges 6 the action of the pins 11 against the edges itl of the arms 13 has a moment about the pivots 14 tending to rotate the arms 13 in the counterclockwise direction as seen in Figure 4, and this moment should be negligibly small.

What I claim is:

l. A mesh structure such as can be used in the envelope of a discharge device, comprising a mesh screen, a mounting in which said screen is mounted for movement in a Vdirection normal to the screen between two limiting positions, and means for holding the screen resiliently in one of said positions so that the mesh can be dislodged and moved to the other limiting position by shock, and means for locking the screen in the other limiting position when the screen is moved thereto.

2. A structure according to claim l, said mounting having a guide-way and said screen having a projection engaging said guide-way to allow the mesh to move between said limiting positions, and comprising a member capable of overlapping the guide-way, spring means for pressing said member into a position overlapping said guide-way, the shape of said member being predetermined to allow said member to be pushed clear of the guideway by said projection only when the projection is in the position corresponding to the rst limiting position of the screen.

3. In the manufacture of a television pick-up tube, the production of a mosaic screen therein by embodying a mesh structure according to claim l in the tube envelope so Ithat the mesh screen is in its first limiting position and adjacent a supporting surface for said mosaic screen, evacuating the envelope, evaporating metal through the interstices of the mesh screen to provide a multiplicity of conductive elements on said supporting surface, thereafter applying a shock to the `envelope to move the mesh screen to its other limiting position so that it can be used as an electrode spaced from the mosaic screen.

References Cited in the tile of this patent UNTTED STATES PATENTS 2,638,563 Donal et al. May 12, 1953 FOREIGN PATENTS 5 89,345 Great Britain June 18, 1947 

